The present invention relates to a television signal digitizing method effective to digitize a television signal by suppressing increase of information quantity at progressive scanning.
Conventionally, as a digitizing method for an interlaced scan television signal, as defined in the CCIR (Comite Consultatif Internationale des Radio-communications) Recommendation 601, a signal digitizing method commonly known as the 4:2:2 (hereinafter referred to as 422) that samples a luminance signal with 13.5 MHz and a chrominance signal with 6.75 MHz in the case of 525 scanning lines and 60 fields/sec or 625 scanning lines and 50 fields/sec is used broadly.
Here, "4" in the above indicates luminance data sampled with 13.5 MHz, "2" indicates chrominance data sampled with 6.75 MHz.
Contrary to this, in case of digitizing a progressive-scanned television signal, since the quantity of information is twice of that of interlace-scanned information, a digitizing method so-called 8:4:4 (hereinafter referred to as 844) that samples a luminance signal with 27 MHz and a chrominance signal with 13.5 MHz is used.
It is to be noted that description on "The operation and maintenance manual" (issued on March, 1991) for "D-1 Signal Converter BKDV 4224DA" by Sony Corp. can be referred for this 844 digitizing method.
Incidentally, in any cases of digitizing methods described above, the sampling frequency for a chrominance signal is lower than that for a luminance signal. The reason is that these methods use the human eye's characteristics that even if the quantity of chrominance information is a half of that of luminance information the deterioration of picture image quality can not be perceived much.
A method called 4:2:0 using this characteristics is also proposed for interlace scan. It is considerable to apply this method to progressive scan to further reduce information quantity.
If applying this method to progressive scan, however, a defect on cost occurs because an additional equipment is necessary to change location of a sampling point.
From the above reason, a new television signal digitizing method has been desired for progressive scan by using the above-mentioned characteristics, that is a method enabling to further reduce information quantity without deterioration of picture image quantity and being compatible with 422 signal, when digitizing progressive-scanned signals.